FWIW, I initially settled on four strips of three for my 120 film (6x6 format); however, since then I acquired a new film scanner, which has a window that's two frames (120mm) long. Thus, when my current supply of PrintFile sleeves runs out, I plan on switching to three strips of four frames. That should make for slightly easier scanning, since there'll be less futzing with the negatives to scan them. Obviously this isn't an issue for an all-analog workflow, and the details will differ even for different scanners, but it's an issue you might want to consider.